This invention relates to valves and more particularly relates to a valve having an improved plug sealing surface and seat.
Valves have been used to control fluid flow for many years. The use of a ball to seal a conically-shaped orifice in a valve, such as the check valves used with chemical injection pumps, is also known. However, there are no plug-guided valves known to the present inventor which use a plug having a curved or radiused sealing surface, or which use a seat having a curved or radiused surface. Rather, the present plug-guided valves use a conically-shaped plug sealing surface and a conically-shaped seat. By "plug-guided", as used herein, is meant a plug having integral structure which guides the plug to and from contact with the seat in such a manner that the plug retains generally the same axial orientation with respect to the seat and that the plug has a defined sealing surface (such as the conically-shaped sealing surface previously mentioned) which engages the seat.
There are problems with the conically-shaped surfaces. For example, if the plug is not perfectly aligned with the seat, the mating cones do not meet properly and, rather than making a continuous contact along the full axial length and around the full circumference of the mating conical surfaces, the cones meet at three discrete contact points (assuming the cones are perfectly shaped), as illustrated in FIG. 1. This distributes all of the loading between the plug and the seat on the discrete contact points which can deform the plug and/or seat and greatly reduce the life of the plug and/or seat. This is particularly likely as the differential pressure across the valve is increased and the diameter of the valve is increased to increase flow capacity, as has been the case with inlet and outlet valves used with high pressure (as much as 20,000 psi) fracturing fluid pumps in the oil industry. As the pressure differential and plug diameter increase, the load exerted on the seat by the plug increases, and any decrease in the contact area between the plug and seat increases the loading per unit of contact area. At the present time, the plugs and seats used with large, high pressure fracturing fluid pumps are often replaced after each use because of deformation created by misalignment and loading of the conically-shaped plug sealing surfaces and seats. This is such a well-known problem that the valves used with fracturing fluid pumps often have stems extending from both the upstream side and the downstream side of the plug to guide and control the alignment of the plug with the seat as closely as possible (and thereby maximize contact area between the plug and seat when the valve is closed). In spite of the use of upstream and downstream stems and guides, there is almost always some misalignment and diminished contact area between the conically shaped plugs and seats.
Therefore, there is a need for a valve having a guided plug which will provide full contact between the plug sealing surface and seat when the plug sealing surface and seat are misaligned in order to keep the loading per unit of contact area as low as possible. There is a need for such a valve which will have contact between the plug sealing surface and seat of approximately the same area regardless of the degree of misalignment between the plug and seat. There is also a need for such a valve which does not need to be guided on both the upstream and downstream sides of the plug.